The following disclosure is directed to systems that use ejection of fluid droplets.
In various industries it is useful to deposit a fluid in a controllable manner onto a substrate by ejecting droplets of the fluid from a fluid ejection module. For example, ink jet printing uses a printhead to produce droplets of ink that are deposited on a substrate, such as paper or transparent film, in response to an electronic digital signal, to form an image on the substrate.
An ink jet printer typically includes an ink path from an ink supply to a printhead that includes nozzles from which ink drops are ejected. Ink drop ejection can be controlled by pressurizing ink in the ink path with an actuator, such as, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatically deflected element. A typical printhead has a line of nozzles with a corresponding array of ink paths and associated actuators, and drop ejection from each nozzle can be independently controlled. In a so-called “drop-on-demand” printhead, each actuator is fired to selectively eject a drop at a specific pixel location of an image, as the printhead and a printing media are moved relative to one another. A high performance printhead may have several hundred nozzles, and the nozzles may have a diameter of 50 microns or less (e.g., 25 microns), may be separated at a pitch of 100-300 nozzles per inch, and may provide drop sizes of approximately 1 to 70 picoliters (pl) or less. Drop ejection frequency is typically 10 kHz or more.
A printhead can include a semiconductor body and a piezoelectric actuator, for example, the printhead described in Hoisington et al., U.S. Pat. No. 5,265,315. The printhead body can be made of silicon, which is etched to define ink chambers. Nozzles can be defined by a separate nozzle plate that is attached to the silicon body. The piezoelectric actuator can have a layer of piezoelectric material that changes geometry, or bends, in response to an applied voltage. The bending of the piezoelectric layer pressurizes ink in a pumping chamber that communicates with a nozzle, and an ink drop is formed.
Fluid drop formation typically is altered by adjusting the waveform parameters such as voltage amplitude, duration of the voltage pulse, slope of the waveform, number of pulses, and other adjustable parameters of the drive pulse delivered to the piezoelectric actuator. The optimal waveform parameters for different fluids vary depending on a particular fluid's physical properties. Typically, the optimal waveform parameters for a specific fluid are determined empirically.